Plastic lug strap



Filed A ril 26, 1965 Oct. 24, 196? c. E; MURRAY 3,348,581-

' PLASTIQ Lue STRAP I a sheets-sheet 1 I U "7 v I 20A 203' INVENTORATTORNEY Oct. 24,

Filed April 26, v1.965-

C. E. MURRAY PLASTIC LUG STRAP v 5 Sheets-Sheet 2 I BY v ATTORNEYINVENTOR United States Patent 3,348,581 PLASTIC LUG STRAP Coyt E.Murray, Gastonia, N;C., assignor to Future Plasfics, Incorporated,Gastonia, N.C., a corporation of North Carolina Filed Apr. 26, 1965,Ser. No. 450,918 2 (Ilaims. (Cl. 139-153) This invention relatesgenerally to the method of manufacturing lug straps used in textile andother machinery. More particularly, my invention relates to lug strapsmade of a plastic such as a high molecular weight polyethylene and tothe method for forming same.

It has long been known in the art of making lug straps that a U-shapedlug strap will wear longer in use on todays high-speed looms if thebowed, impact-receiving web portion of the strap is thicker than thesides. Thickening of the Web has previously been accomplished by fixingan impact-absorbing plug to the inner surface of the web.

Traditionally, lug straps have been formed from lengths of a suitablematerial by bending said lengths into U- shapes and treating ormechanically fixing the formed strap so that the said U-shape isretained during use. United States Letters Patent No. 2,216,999 to Bacondiscloses a method of making lug straps with a thickened web from afiat, woven webbing impregnated with an excess quantity of rubber orother thermo-setting materials by so molding the impregnated webbing asto force additional impregnant from the side portions of the lug strapinto the web and to shape the excess impregnant in the web of the strapto provide the desired thickened area or cushion.

The known methods of manufacturing lug straps from polyethylene of ahigh molecular weight or from other suitable plastic materials eitherhave involved the provisionof a separate plug and the subsequentaflixing of the plug to the inner surface of the web by suitable means,or have involved the formation of the lug strap from a blank stockhaving a medial portion which is thicker than the end portions which areto become the sides of the formed strap.

The use of separate plugs necessitates the extra manufacturing step ofmechanically affixing the plug to the formed lug strap blank or offorming the strap about the plug under pressure and temperatureconditions conducive to some polymerization between the molecules of theplug and the molecules of the blank. Unless there has been suflicientpolymerization between the molecules of the wtih the web. I

The use of non-uniformly thick lengths of plastic has beenunsatisfactory in that complicated and costly machinery for forming samemay be required or else expensive and time consuming machining ofuniformly thick pieces into desired shapes is necessary. In eithereventthere is a consequential waste of material.

Unsuccessful attempts have been made to manufacture lug straps with anintegral plug by injection molding of high molecular weightpolyethylene. The resultant product has proven unsatisfactory in usebecause of a high form thickness throughout its length, which method hasthe attendant advantages of avoiding the use of separateice 1y formedplugs or cushions; and of avoiding the necessity of providing lengths ofstock having portions of varying thicknesses with a consequent waste ofmaterial.

It is a still further object of this invention to provide a method ofmanufacturing plastic lug straps wherein substantial economies inmachinery, labor, and materials can be effected. i

It is another object of this invention to provide an improved lug strapwhich includes an integral plug and wherein the entire lug strap andplug are formed from a length of high molecular weight polyethylenewhich is of substantially the same uniform width and thicknessthroughout its length as the legs of the finished lug strap.

It is a more specific object 'of the invention to provide an improvedmethod of making an improved lug strap with an integral plug from highmolecular weight polyethylene of the type described wherein the improvedmethod of defining the integral plug results in a substantial increasein tensile strength of the plug due to the orientation of the molecularchain in the direction ofthe impact to which the plug is subjected inuse. The increased tensile strength of the plug greatly improves thewear and abrasion properties of the lug strap and significantlyincreases the useful life of the strap.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds, when taken in connection withthe accompanying drawings, in

- which:

FIGURE 1 is a perspective view of a length of plastic stock ofsubstantially uniform width and thickness throughout its length fromwhich the improved lug strap is formed;

FIGURE 2 is a perspective view illustrating the initial step of bendingthe stock into a U-shaped configuration;

FIGURE 3 is a plan view of the U-shaped strap loosely positioned withina schematically illustrated mold;

FIGURES 4 and 5 are plan views of the strap within the schematicallyillustrated mold at sequential stages during the molding operation;

FIGURE 6 is a perspective view of the completed lug strap removed fromthe mold;

FIGURE 7 is a sectional view with parts broken away taken substantiallyalong the line 7-7 in FIGURE 3 and omitting the .lug strap blank;

FIGURE 8 is a somewhat schematic perspective view of a mold used inpracticing the invention; and

FIGURE 9 is a sectional plan view taken substantially along the line 9-9in FIGURE 8.

According to the preferred form of the present invention a'charge ofpowdered high molecular weight polyethylene having a molecular weight inexcess of one million is placed in an extruder and heated above thefusion point. Bar stock is extruded under a sufficiently hightemperature to polymerize the polyethylene. While the bar stock is at atemperature within its fusion range of 200- 500 F., wherein the plasticstock is sufliciently softened to be bonded or welded, it is cut intodesired lengths to define blanks 10, each 'blank being of substantiallyuniform width and thickness throughout its length, and from which thelug straps are to be formed according to the invention. While it ispreferred, in an integrated operation, to shape and define the lugstraps from bar stock which still retains the heat from the extruder, itis to be understood that it is within the spirit of the invention toform the lug straps from inventories of extruded bar stock which hasbeen allowed to cool and reheated subsequent to its extrusion, or to cutstock of the desired dimensions from slab material to define a blank 10and reheat it.

In any event, the method and product of the invention are obtained whilethe blank 10 is at a temperature within the said fusion range of thehigh molecular weight poly- 3 ethylene, preferably at a temperaturebetween 289 to 350 F.

While the blank is still within the said fushion range, it is manuallybent into generally U-shaped configuration as shown in FIGURE 2. Uponbeing bent into U-shaped configuration, the blank 10 com-prises legs orsides 11 and 12 interconnected by a web 13. The blank 10, while still ata temperature above its fusion point is loosely placed in an open mold14 comprising a fixed core 15, a pair of movable side plates 16 and 17and a movable end plate 18.

The other end of the mold is closed by a'fixed end plate 19 which abutsthe corresponding end of the core 15. The mold 14 additionally includesa base 30 to which the core and fixed end plate 19 are fixed. Themovable side plates 16 and 17 and the movable end plate 18 may bereciprocated by respective hydraulic cylinders 31a, 31b, and 310 andhydraulic pistons 32a, 32b, and 320. The cylinders 31a, 31b, and 310 arefixed against movement relative to the base 30 as by stops or abutments33a, 33b, and 330.

The mold also includes a top plate 35 fixed to the lower end of a ram orpiston 32d (FIGURE 8). The piston 32d is reciprocable within a hydrauliccylinder 31d, the upper end of which depends from a stationarysupporting plate 36. The support plate 36 is held in fixed spacedrelation to the base 30 by a plurality of tubular leg-s 37 (FIG- URE 8),each of which loosely penetrate the movable top plate 35 of the mold 14,and are fixed at their respective ends to the base 30 and the supportplate 36.

After the U-shaped blank 10 is loosely placed in the open mold 14, thetop plate 35 is moved downwardly under hydraulic pressure to close thetop of the mold. The hydraulic rams 32a and 32c are then actuated tomove their respective side plates 16 and 17 inwardly to clamp the legsof the U-shaped blank 10 against the core 15. Next, the end plate 18 ismoved inwardly under hydraulic pressure imparted to the ram 32b to shapethe web of the lug strap.

The inner limit of the inward movement of the side plates 16 and 17 andthe movable end plate 18 is predetermined to coincide with the desiredthickness of the legs and web of the finished lug strap. In general, thethickness of the legs of the finished lug strap corresponds to thethickness of the initial bar stock and the thickness of the web in thefinished lug strap is in the order of one and one-half to two and a halftimes the thickness of the legs.

As most clearly seen in FIGURE 3, the inner surface 20 of the web 13 isdeformed into alternate transverse projections and depressions 20A and20B as a result of the compression to which the surface 20 is subjectedduring bending of the blank into U-shaped configuration. The end of thecore 15 adjacent the end plate 18 has a concave surface 21 (FIGURE 7)with which the inner surface 20 of the web 13 is adapted to engage underinward pressure of the mold end plate 18.

When loosely placed in the mold, the outer surface of the web 13 islocated at a point spaced beyond the concave surface 21 on the core, thelocation of the outer surface of the web being designated by the line Ain FIG- URE 3. Arranged in this manner, the inner surface 20 of the web13 is likewise spaced from the end 21 of the core 15 to define a cavityC between the core and the inner surface 20 when the blank 10 isinitially positioned in the mold as shown in FIGURE 3.

Continued inward pressure of the end plate 18 moves the outer surface ofthe web 13 away from the line A and toward the end surface 21 of thecore 15 (FIGURES 4 and 5). It is apparent from the sequential stepsillustrated in FIGURES 3, 4, and 5 that the continued inward movement ofthe end plate 18 collapses and reorients the web causing it to move intothe cavity C until the projections 20A on the inner surface of the webenlarge under inward movement of the end plate 18 and engage the concavesurface 21 of the core 15 (FIGURE 5). The cavity C is gradually filledin and closed by the thickening web as the molecular structure of theplastic is reoriented in the mold. Meanwhile, the sides or legs 11 and12 have been subjected to pressure sufficient to serrate the inner endsurfaces of the legs 11 and 12, but the pressure is not sufficient tosignificantly change the dimensions of the legs as in flow molding.Thus, when removed from the mold the lug strap as shown in FIGURE 6 haslegs of substantially the same dimensions as the thickness and width ofthe bar stock from which the blank 10 was formed, while the web 13 withits integral plug is much thicker.

In order to help in maintaining the plastic at a temperature which willpermit reorientation of the web under pressure of the mold, and toimprove the surface appearance of the strap, the mold is desirablyheated to a temperature within the range of to 230 F., preferably atabout 180 F., for controlled cooling of the blank while in the mold. Themold can be used at room temperature, if desired, but experience hasshown that the surface appearance of the lug strap is improved byheating the mold as indicated.

In practice, the blank is molded under a molding pressure of from about200 to 300 psi. for one to four minutes. If desired, the moldingpressure can be incresed as high as practical, such as 5000 psi, and themolding time can be lengthened indefinitely; but an increase in pressureand time does not improve the product and the invention is not limitedto a top range of molding pressure and time.

The slots 40a. and 40b in the serrated end portions of the legs 11 and12 (FIGURE 6) may be cut after the lug strap is removed from the mold.Alternatively, if desired, the mold may be equipped with suitablepunches or dyes to form the slots 40a and 40b during the postformingmolding operation.

The completed lug strap has exhibited unusual wearresistant propertiesin use and these properties are attributed in part to the reorientationof the molecular structure during the post-forming molding operation atwhich time the web is reoriented and thickened in the manner describedand illustrated.

The term plastic as used throughout the specification and claims refersto high molecular weight polyethylene and/ or to any material which isits equivalent, and the invention is not limited specifically to the useof high molecular Weight polyethylene.

In the drawings and specification there have been set forth preferredembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being defined in theclaims.

I claim:

1. A lug strap comprising a pair of spaced legs and an enthi-ckened webinterconnecting corresponding ends of the legs and formed from highmolecular weight polyethylene having a molecular weight of at least1,000,000, and the molecular chains in said high molecular weightpolyethylene web extending in a direction parallel to said legs, thusincreasing the strength of said web.

2. A lug strap according to claim 1 wherein the enthickened web isintegral with the legs.

References Cited UNITED STATES PATENTS 2,216,999 10/1940 Bacon 139l532,325,060 7/1943 Ingersoll. 3,019,486 2/ 1962 Stinson 264-291 (Otherreferences on following page) 5 FOREIGN PATENTS 567,192 10/1958 Belgium.978,052 12/1964 Great Britain.

OTHER REFERENCES Textile Industries: Vol. 125, No. 12, November 1961,Smith Pub. Co., Atlanta, Ga., p. 59.

6 Textile Industries: Vol. 127, N0. 6, June 1963, Smith Pub. Co.,Atlanta, Ga., pp. 48-49.

Textile Industries: Vol. 127, N0. 2, February 1963, Smith Pub. 00.,Atlanta, Ga., pp. 36-37.

MERVIN STEIN, Primary Examiner.

J. KEE CHI, Assistant Examiner.

1. A LUG STRAP COMPRISING A PAIR OF SPACED LEGS AND AN ENTHICKENED WEBINTERCONNECTING CORRESPONDING ENDS OF THE LEGS AND FORMED FROM HIGHMOLECULAR WEIGHT POLYETHYLENE HAVING A MOLECULAR WEIGHT OF AT LEAST1,000,000, AND THE MOLECULAR CHAINS IN SAID HIGH MOLECULAR WEIGHTPOLYETHYLENE WEB EXTENDING IN A DIRECTION PARALLEL TO SAID LEGS, THUSINCREASING THE STRENGTH OF SAID WEB.